Various types of medical devices are employed to monitor electrical or other activity of the heart and to provide therapy to the heart in response to the detection of irregular cardiac rhythms. Such devices may be implantable beneath the skin of a patient, i.e., in the patient's chest. Such implantable devices include a hermetically sealed canister containing electronic circuitry for implementing the functions of the device, one or more electrodes implanted in one or more of the chambers of the heart, or in close proximity thereto, and leads for connecting the electrodes to the circuitry within the device canister. The device circuitry includes circuitry for detecting electrical signals produced by the heart, which signals are picked up at the electrodes, along with circuitry, typically implemented in a microprocessor, for analyzing the thus-detected cardiac signals. The device may also include circuitry for providing therapy in the form of electric shock signals applied to the heart. Such signals are provided to the heart, via the leads and electrodes mounted in the heart, in response to the detection of an irregular cardiac rhythm by the analysis circuitry based on the detected cardiac activity signals. The implantable device may also include a transmitter/receiver, for transmitting cardiac activity and other information to an external device for, e.g., storage and/or further analysis, and for receiving information, such as programming instructions, from the external device via, for example, an RF link.
An example of such an implantable cardiac device is an automatic implantable cardioverter defibrillator (AICD) for treating atrial arrhythmias, e.g., atrial tachycardia, fibrillation, flutter, etc. (The functionality of an atrial AICD may be combined with those of a bradycardia pacemaker, ventricular defibrillator, etc.) Atrial arrhythmias are probably the most common cardiac arrhythmia. Although atrial arrhythmias are not usually life-threatening, patients with atrial arrhythmias generally experience palpitations of the heart, and may experience dizziness or even loss of consciousness. Atrial arrhythmias, such as atrial fibrillation, also have been associated with strokes and other conditions. Atrial arrhythmias can occur suddenly. Implantable atrial cardioverter defibrillators are programmed to detect the onset of atrial arrhythmias and to provide an appropriate electrical shock therapy to the atria to terminate the atrial arrhythmia. The atrial shock therapy to be provided may depend upon the type of atrial arrhythmia detected, e.g., atrial tachycardia versus atrial fibrillation. Shock therapy provided by an implantable atrial cardioverter defibrillator may include a relatively high voltage level atrial defibrillation or cardioversion pulse, which is typically delivered to the atria in synchronism with a detected or paced ventricular activation, to terminate atrial fibrillation or flutter. Atrial antitachycardia pacing may be applied by the implantable device to terminate atrial tachycardia. Atrial antitachycardia pacing typically involves a train of pacing pulses applied to the atria at a rate slightly higher than the rate of the tachycardia.
Various systems and methods have been developed to allow patients having implanted atrial cardioverter defibrillators to monitor and control, to at least some degree, operation of the implanted device. For example, U.S. Pat. No. 5,490,862 describes an implantable atrial defibrillator which may be programmed to operate in a patient activated mode of operation. In the patient activated mode, an atrial fibrillation intervention sequence is performed by the implanted device in response to the receipt of a sequence command generated from external to the patient. The sequence command may be generated, for example, by an external magnet applied by the patient to near the implantation site, to close and then open a reed switch mounted in the implanted device and coupled to the device microprocessor. The intervention sequence thus initiated by the patient, when he believes he is experiencing an atrial arrhythmia, includes atrial fibrillation detection by the implanted device and, if atrial fibrillation is confirmed, the application of cardioverting electrical energy to the atria.
U.S. Pat. No. 5,674,249 describes the use of a portable communication device which allows a patient to monitor and control the operation of an implanted atrial defibrillator. The portable communication device, which may be dimensioned to be hand held by a patient, includes a transmitter/receiver for communicating with the implanted device via a telemetry (e.g., RF) link. In this system, an atrial fibrillation intervention sequence may be initiated in an implanted device in response to a sequence command generated from the portable communication device. The patient may also use the portable communication device to program the implanted device into an automatic mode wherein the intervention sequence is initiated automatically at predetermined times. The handheld portable communication device receives an acknowledgment signal from the implanted device when a command signal sent from the communication device is received by the implanted device. The receipt of the acknowledgment signal by the portable handheld communication device is displayed to the patient on the device. The display includes a description of the task being performed by the implanted device in response to the command signal sent by the patient. Thus, a patient is able to both monitor and control operation of an implanted cardiac device to some degree.
U.S. Pat. No. 5,999,851 describes an implantable atrial defibrillator which includes an atrial fibrillation detection only mode of operation. In this mode, atrial fibrillation detection is initiated in the implanted device by a command signal sent from an external patient operated communication device, which is in communication with the implanted defibrillator via a telemetry (e.g., RF) link. If atrial fibrillation is detected by the implanted atrial defibrillator, an appropriate signal is communicated to the patient operated communication device, and a visual and/or audible message is provided by the communication device to the patient to indicate whether or not atrial fibrillation is detected. In this detection only mode, a further signal must be provided from the communication device to the implanted device to initiate cardioversion therapy, preferably after continued atrial fibrillation is confirmed by the implanted device.
In each of the systems described above, atrial fibrillation detection, or atrial fibrillation detection followed by atrial shock therapy, if required, may be initiated by a patient using an external communication device. To monitor the progress of an ongoing atrial arrhythmia event in such systems, a patient must repeatedly signal the implanted device to reinitiate atrial fibrillation detection. Furthermore, to both monitor the status of an atrial arrhythmia detected by the implanted device and control the providing of shock therapy to the atria by the implanted device a relatively complicated external communication device employing a telemetry link is used to provide a variety of control signals from the communication device to the implanted device.
What is desired is an atrial shock therapy system which allows a patient to monitor the status of an ongoing atrial arrhythmia event without requiring repeated reinitiation by the patient of atrial arrhythmia detection. Preferably, a relatively simple and inexpensive patient controlled activator or communication device may be employed by the patient both to monitor atrial event status as determined by an implanted device as well as to control the providing of atrial shock therapy by the implanted device.